REPRODUCTIVE ORGANS.—_Leptoplana_ is hermaphrodite, and, as in most hermaphrodites, the reproductive organs are complicated. The male organs are the first to ripen, but this does not appear to prevent an overlapping of the periods of maturity of the male and female products, so that when the eggs are being laid, the male organs are, apparently, still in a functional state. The principal parts are seen in Fig. 5. The very numerous _testes_ (_te_) are placed ventrally, and are connected with fine vasa _efferentia_ (_ve_), which form a delicate network opening at various points into the two _vasa deferentia_ (_vd_). These tubes, especially when distended with spermatozoa, may easily be seen (Fig. 2, _vd_) converging at the base of the penis, and connected posteriorly by a loop that runs behind the female genital pore (Fig. 5). The _penis_ (_pe_) is pyriform and muscular, and is divided into two chambers, a large upper one for the spermatozoa, and a smaller lower one for the secretion of a special {16}"prostate" gland. The apex of the penis is eversible and not merely protrusible, being turned inside out when evaginated. The _ovaries_ (Fig. 5, _ov_) are numerous and somewhat spherical. They are dorsally placed, but when fully developed extend deeply wherever they can find room to do so, and they not only furnish the ova, but elaborate food-yolk in the ova, as there are no special yolk-glands. The slender _oviducts_ (_od_) open at several points into the "uterus" (_ut_) (a misnomer, as no development takes place within it), which encircles the pharynx, and opens by a single duct into the _vagina_ (_va_). Here the ova are probably fertilised, and one by one invested by the _shell-gland_ (_sg_) with a secretion which hardens and forms a resistant shell. They are then laid in plate-like masses which are attached to stones or shells. The development is a direct one, and the young _Leptoplana_, which hatches in about three weeks, has the outline of a spherical triangle, and possesses most of the organs of the adult. After leading a floating life for a few weeks it probably attains maturity in about nine months. CLASSIFICATION, HABITS, AND STRUCTURE OF THE POLYCLADIDA. The Polyclads were so called by Lang on account of the numerous primary branches of their intestine. They are free-living, purely marine Platyhelminthes, possessing multiple ovaries, distinct male and female genital pores (Digonopora), but no yolk-glands. The eggs are small, and in many cases give rise to a distinct larval form, known as "Müller's larva" (Fig. 12). The Polyclads, with one exception,[24] fall into two sub-groups, Acotylea and Cotylea:— Character. Acotylea. Cotylea. Sucker A sucker absent.[25] A sucker always present (Figs. 8, D, _s_; 7, A, _sc_).